Prevalence, incidence and etiology

Hamstring muscle strain injuries (HMSI) are common in sports that involve sprinting (Orchard et al., 1997), acceleration, deceleration, rapid change in direction and jumping (Devlin, 2000; Drezner, 2003). For this blog, Grant Freckelton discusses the prevalence, etiology, and identification of risk factors for such injuries based on a research paper he was involved in in 2013.

These injuries can result in substantial time lost from sport and commonly recur (Orchard & Seward, 2008; Upton et al., 1996). In the Australian Football League (AFL) hamstring injuries are the most prevalent injury with a 21 years of age, with a mean of 6 new injuries per club per season causing 20.4 missed matches per club per season. There is also a high average recurrence rate of 26% (Orchard et al., 2013).

Hamstring injuries during sprinting are proposed to occur during the terminal swing phase of running as a consequence of an eccentric contraction (Schache et al., 2009; Heiderscheit et al., 2005). Askling, et al., (2006) has proposed two distinct mechanisms of hamstring injuries.

Type 1 involve high intensity runningwith injury occurring during late swing phase involving the proximal musculotendinous junction of the long head of biceps femoris.

Type 2 is described as a stretching of the hamstring complex due to extreme joint positions involving mostly semimembranosus and the proximal tendon (Yu et al, 2008; Askling et al, 2006).

The majority of hamstring injuries occur at the biceps femoris (BF) long head (Koulouris & Connell, 2005; De Smet & Best, 2000; Croisier, et al., 2004). During the 2011 AFL season 84% of all hamstring injuries occurred at biceps femoris, 10% at semimembranosus and 4.3% at semitendinosus (Pizzari et al. 2012). Of these 27.3% of all hamstring strains occurred at the distal musculotendinous junction (MTJ) of BF, 19.7% at proximal MTJ of BF and 18.2% in the belly of BF (Pizzari et al. 2012).

Risk factors

Many papers have examined potential risk factors for HMSI, with age and previous hamstring strain being accepted as risk factors, and many others inconsistently identified as contributing to the injury.A systematic review and meta-analysis into risk factors for hamstring injury identified older age, increased quadriceps peak torque and past history of hamstring injury were associated with increased risk of hamstring muscle strain injuries. Other strength measures such as hamstring:quadriceps ratio, commonly perceived to be predictive of injury, were not associated with hamstring injury (Freckleton & Pizzari, 2013).

The subjective assessment is key to correctly diagnose an injury. Players with a hamstring injury will report sudden onset of pain localised to the hamstring region with a clear mechanism or incident. There is significant disability at time of injury (Pizzari, et al., 2010). Previous injury history, particularly previous hamstring injury is also important, as this is one of the major risk factors for future hamstring injuries (Freckleton, et al., 2012).

Clinical examination for determining hamstring injury is considered to be reliable and accurate (Schneider-Kolsky, et al., 2006). A hamstring injury can be defined as having positive clinical signs and symptoms including (Bennell, et al., 1999):

Immediate onset of posterior thigh pain,

Tenderness on palpation,

Reproduction of pain on stretch of hamstring,

Reduced straight leg raise ROM,

Reproduction of pain and reduced strength on resisted active contraction of hamstrings, and

Unable to continue playing or training and miss at least one game due to the hamstring injury.

The physical examination should include lumbar spine AROM, Slump, SLR, active knee extension test (AKE), passive hamstring muscle stretch and palpation of pelvic musculature for trigger points and reproduction of posterior thigh pain. Resisted contraction of the hamstrings should be tested in multiple positions of knee flexion (Brukner & Khan, 2006). Palpation is the most important aspect of the physical examination to help identify location and severity of the injury (Pizzari, et al., 2010).

(Brukner & Khan, 2006)

A recent study investigated the use of the single leg hamstring bridge (SLHB) as a clinical test in predicting hamstring injuries in football players. The single leg hamstring bridge tests the hamstring muscles in a functional position similar to terminal swing and assesses endurance parameters rather than peak torque. This study demonstrated a significant deficit in preseason SLHB scores on the right leg of players that subsequently sustained a right-sided hamstring injury.

Age, previous knee injury and a history of hamstring injury were other risk factors supported in the study, which also had a negative impact on SLHB scores. Due to the confounding variables and low injury rate in this study, further research is required (Freckleton, et al., 2013). The SLHB test could be used to screen and identify athletes who are potentially at risk of sustaining a hamstring injury. It may also be used to evaluate the readiness of an athlete to return to sport.

Pizzari, T., Wilde, V., & Coburn, P. (2010). Management of hamstring muscle strain injuries in the Australian Football League (AFL): A survey of current practice. Journal of Science and Medicine in Sport, 13, e76.